Display apparatus and its control method
A display apparatus includes a plurality of light modulation elements configured to modulate light from a light source for each color, and a driver configured to drive the plurality of light modulation elements using drive signals in accordance with a digital drive method. The driver makes different from one another start timings of the drive signals corresponding to one frame period for the plurality of light modulation elements.
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The present invention relates to a display apparatus of a digital drive method.
Description of the Related ArtAlong with progresses in a small configuration and a high resolution of a light modulation element, a display apparatus configured to drive the light modulation element using a drive signal in accordance with a digital drive method has been proposed. Where a plurality of light modulation elements are driven by the digital drive method, color breaking may occur.
Japanese Patent Laid-Open No. (“JP”) 2011-118067 discloses a configuration that can reduce the color break in an image display apparatus that drives a reflection type liquid crystal panel in a field sequential color method.
However, in order to reduce the color break generated in the digital drive method, the configuration of the image display apparatus in the field sequential color method disclosed in JP 2011-118067 is inapplicable to the display apparatus configured to drive the plurality of light modulation elements by the digital drive method.
SUMMARY OF THE INVENTIONThe present invention provides a display apparatus and its control method which can reduce a color break caused by a digital drive method.
A display apparatus according to the present invention includes a plurality of light modulation elements configured to modulate light from a light source for each color, and a driver configured to drive the plurality of light modulation element using drive signals in accordance with a digital drive method. The driver makes different from one another start timings of the drive signals corresponding to one frame period for the plurality of light modulation elements.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Referring now to the accompanying drawings, a detailed description will be given of an embodiment of the present invention.
Referring now to
The PWM (pulse width modulation) drive method illustrated in
As illustrated in
The color braking may occur in this liquid crystal display apparatus in the 3LCD method for driving a plurality of (three) liquid crystal display elements by a digital drive method. For example, in displaying the gray tone, as illustrated in
In
Referring now to
An image signal (external image signal) output from the video player 302 is input into the liquid crystal projector 301 via a video cable 303. The liquid crystal projector 301 generates an image signal (output signal) suitable for display based on the input image signal (input signal), and projects an image 305 corresponding to the output signal onto a projected surface 304, such as a screen.
Referring now to
The liquid crystal driver 403 drives a plurality of liquid crystal display elements 404, such as the RGB liquid crystal display elements, for example, liquid crystal panels, using the drive signals in accordance with a digital drive method (PWM drive method). The liquid crystal display element 404 modulates light from the light source 405 for each color. The liquid crystal display element 404 is provided for each of the RGB colors, and each liquid crystal display element 404 generates an image of each color (continuous frame images). The light from the light source 405 is separated into the three RGB color light fluxes by an illumination optical system 406, and input into and modulated by the three liquid crystal display elements 404. The three modulated color light fluxes are combined into one light flux and projected by a projection optical system 407.
The liquid crystal driver 403 includes a delay circuit 402. The delay circuit 402 delays the start timing Ts of the drive signal for driving at least one of the plurality of liquid crystal display elements 404. In other words, the delay circuit 402 provides a predetermined delay time to a start timing for at least one PWM drive in the RGB (output timing of the drive signal). Then, the delay circuit 402 generates the PWM pattern (drive signal) for the ON/OFF control according to each output tone, and outputs the PWM pattern to the corresponding liquid crystal display element 404. Thus, in this embodiment, the liquid crystal driver 403 shifts from one another the start timings Ts for the three liquid crystal display elements 404 of the drive signals corresponding to one frame period. A CPU 408 as a main controller controls the image processor 401 and the delay circuit 402, as well as controlling driving of the light source 405 and driving of the liquid crystal display elements 404 by the liquid crystal driver 403.
Referring now to
In
Referring now to
In
The color break can be reduced by the delay times 901 and 902 as illustrated in
In this embodiment, the liquid crystal driver 403 shifts the start timings of the drive signals so that a plurality of color light emission centroids of the plurality of liquid crystal display elements 404 (centroids of the optical response waveforms) approach to one another. The start timings may be shifted so that the plurality of color light emission centroids accord with one another. The optimal delay time is different according to the color and tone to be displayed by the liquid crystal display apparatus. Hence, the delay circuit 402 may control (vary) the delay time according to the color or the tone.
The plurality of liquid crystal display elements 404 in this embodiment includes a first liquid crystal display element configured to modulate light in the R band, a second liquid crystal display element configured to modulate light in the G band, and a third liquid crystal display element configured to modulate light in the B band. The liquid crystal driver 403 delays the start timing of the second liquid crystal display element relative to the start timing of the first liquid crystal display element. The liquid crystal driver 403 delays the start timing of the second liquid crystal display element relative to the start timing of the third liquid crystal display element. The liquid crystal driver 403 delays the start timing of the third liquid crystal display element relative to the start timing of the first liquid crystal display element. However, this embodiment is not limited to this example, and can arbitrarily vary a relationship of the start timing among the liquid crystal display elements so as to reduce the color break.
Now assume that ΔT is a shift time (delay time) of the start timing of the drive signal corresponding to the one frame period for at least one of the plurality of liquid crystal display elements, and Ta is a continuous OFF period in the one frame period up to the end timing in the one frame period. At this time, ΔT≤Ta is to be satisfied. Referring now to
When the responsiveness of the liquid crystal display element is considered as described above, the delay time may be longer than the shift time (delay time) necessary to accord the centers of the ON period of the drive signal with each other. In other words, the shift time ΔT provided by the delay circuit 402 may satisfy ΔT≥Ta/2. In conclusion, the shift time ΔT may satisfy the conditional expression of Ta/2≤ΔT≤Ta.
This embodiment can provide a display apparatus and its control method which can reduce a color break caused by the digital drive method.
While this embodiment drives the liquid crystal display element using the PWM drive method as a digital drive method, the present invention is not limited to this embodiment and may use the digital drive method other than the PWM drive method. In addition, while this embodiment shifts (delays) the start timing of the drive signal corresponding to the one period using the delay circuit for at least one liquid crystal display element, the present invention is not limited to this embodiment. For example, the start timing may be shifted by another method, such as a shift control by the CPU 408. Moreover, this embodiment uses the liquid crystal display element as a light modulation element, but may use a digitally drivable light modulation element, such as a DMD (digital mirror device).
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2016-198256, filed Oct. 6, 2016, which is hereby incorporated by reference herein in its entirety.
Claims
1. A display apparatus comprising:
- a plurality of light modulation elements each configured to modulate light from a light source for a respective color; and
- a driver configured to drive the plurality of light modulation elements using drive signals in accordance with a digital drive method,
- wherein the driver is configured to make different, from one another, start timings of the drive signals corresponding to one frame period for the plurality of light modulation elements,
- wherein the driver is configured to generate the drive signals of the respective light modulation elements to control an ON period and an OFF period based on a tone of an input image in each of a plurality of subframes contained in the one frame period, and
- wherein in displaying a tone corresponding to a maximum tone of the input image, parts of the ON periods of the drive signals overlap with each other, and at least one of sums of the ON periods of the drive signals is shorter than the one frame period.
2. The display apparatus according to claim 1, wherein the driver includes a delay circuit configured to delay the start timings of the drive signals for driving at least one of the plurality of light modulation elements.
3. The display apparatus according to claim 2, wherein the delay circuit is configured to vary a delay time of the start timing according to a color or a tone.
4. The display apparatus according to claim 1, wherein the driver is configured to make different, from one another, the start timings of the drive signals so that light emission centroids for a plurality of colors output from the plurality of light modulation elements approach one another.
5. The display apparatus according to claim 1, wherein the digital drive method is a pulse width modulation (PWM) drive method.
6. The display apparatus according to claim 5, wherein the following conditional expression is satisfied:
- Ta/2≤ΔT≤Ta,
- where ΔT is a shift time of the start timing of the drive signal, and Ta is a continuous OFF period in the one frame period up to an end timing of the one frame period, each of ΔT and Ta corresponding to the one frame period for at least one of the plurality of light modulation elements.
7. The display apparatus according to claim 1, wherein the plurality of light modulation elements include a first light modulation element configured to modulate light in a red (R) band, a second light modulation element configured to modulate light in a green (G) band, and a third light modulation element configured to modulate light in a blue (B) band.
8. The display apparatus according to claim 7, wherein the driver is configured to delay the start timing for the second light modulation element relative to the start timing for the first light modulation element.
9. The display apparatus according to claim 7, wherein the driver is configured to delay the start timing for the second light modulation element relative to the start timing for the third light modulation element.
10. The display apparatus according to claim 7, wherein the driver is configured to delay the start timing for the third light modulation element relative to the start timing for the first light modulation element.
11. A control method for a display apparatus, the control method comprising the steps of:
- modulating light from a light source for each color by driving a plurality of light modulation elements using drive signals in accordance with a digital drive method;
- combining and projecting modulated light fluxes; and
- driving the plurality of light modulation elements to shift, from one another, the start timings of the drive signals corresponding to one frame period for the plurality of light modulation elements,
- wherein the driving step generates the drive signals of the respective light modulation elements to control an ON period and an OFF period based on a tone of an input image in each of a plurality of subframes contained in the one frame period, and
- wherein in displaying a tone corresponding to a maximum tone of the input image, parts of the ON periods of the drive signals overlap with each other, and at least one of sums of the ON periods of the drive signals is shorter than the one frame period.
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- Office Action issued in Japanese Application No. 2016-198256 dated Aug. 7, 2018. English translation provided.
- Extended European Search Report issued in European Appln. No. 17001618.2 dated Jan. 26, 2018.
Type: Grant
Filed: Oct 3, 2017
Date of Patent: Jul 30, 2019
Patent Publication Number: 20180102098
Assignee: CANON KABUSHIKI KAISHA (Tokyo)
Inventor: Masao Ono (Shimotsuke)
Primary Examiner: Duane N Taylor, Jr.
Application Number: 15/723,708
International Classification: G09G 3/34 (20060101); G09G 3/20 (20060101); G09G 3/36 (20060101); G09G 3/00 (20060101);